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Tractor Pulling Discussion Forum

HI-TECH COMPRESION QUESTIONS-FOR THOSE WHO KNOW

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Clarence Bareni

01-21-2005 19:23:00




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I'm going to isolate several question's,and ask for simple answer's.
My question's are !
If you take a 4 cylinder engine that has a base compression ratoi of 6.1-1 and change the ratio to
9.1-1 , what is the net end result!
1) let's assume that the correct gasoline will be used, with the rite spark plug heat range to burn fuel.
2) We will leave fuel delivery system the same.
3) RPM range will stay the same.
4) Stroke will stay the same.
Will the tractor as described have less lugging capacity or more because of compression (alone)
MY ULTIMATE QUESTION IS ? When compression is so low, by todays standards, is there a nice amout of low end torque that can be created just by bringing compression up to todays fuel standards ?
Have you built it and do you have a conclusive answer !

Thank you
Bud barenie

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acwc

01-22-2005 08:39:05




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 Re: HI-TECH COMPRESION QUESTIONS-FOR THOSE WHO KNO in reply to Clarence Barenie, 01-21-2005 19:23:00  
Well with all the talk about comp ratio what is the best all round comp to try and get? Or are there to many variables.



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buickanddeere

01-22-2005 08:37:43




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 Re: HI-TECH COMPRESION QUESTIONS-FOR THOSE WHO KNO in reply to Clarence Barenie, 01-21-2005 19:23:00  
You are increasing the mechanical efficiency of the engine. More compression also means a high expansion raio on the power stroke. In short, more of the energy from the heat and pressure of compression is used to push the piston before the exhaust valve opens. This is why steam piston engines use a larger secondary cylinder which is fed from the exhaust of the primary cylinder. And why steam turbines systems use a secondary low pressure turbine fed for the exhuast of the 1st stage high pressure turbine. There is a point of dimishing returns where say a jump from 5 to 1 to 8 to 1 gains "x" power. However a jump from 10 to 1 to 13 to 1 has a much lower HP gain and detonation is a now a nightmare.

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MMark

01-22-2005 07:57:05




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 Re: HI-TECH COMPRESION QUESTIONS-FOR THOSE WHO KNO in reply to Clarence Barenie, 01-21-2005 19:23:00  
I'm a engineer by trade and a tractor puller/restorer at heart. I have looked for years to find some kind of formulas to guestimate potential performance and have found bits and pieces here and there but nothing set in stone. However, I have found the following formula to be pretty close and have tested it several times and seems to be in the ballpark. Take the compression ratio you want to achieve divide it by what you have, take that number and multiply it by the horsepower you now have. then you will have to muliply that number by the volumetric efficiency. VE is normally 70 to 85% in antique tractors.

Now that I have confused you lets use Marty's F14 numbers. He had 5 to 1 comp. and 23.5 hp. He increased comp. to 7.64 to 1. I will use 85% VE because he said it was real good on efficiency.

7.64 divided by 5 = 1.528
1.528 multiplied by 23.5 = 35.9 hp
35.9 multiplied by .85 = 30.5

30.5 is what he saw on the dyno.

As Chad said you will have to change carb and advance setings. This formula assumes you are using the same rpm's, cam and manifolds. It is normally within 2 to 5%. I have had cases where it made close to the same hp. This normally means you have reached the max efficiency of your intake or exhaust tracts.

I hope this helps. By no means take this as the gospel. It is just a lttle bench racing formula I have come up with to give you an idea of what you can expect.

P.S. you can als use this for displacement increases. just substitute cu.in for the conpression data. Its not as close but will get you more ballpark data.

Mark Damewood

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NP

01-22-2005 11:04:47




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 Re: HI-TECH COMPRESION QUESTIONS-FOR THOSE WHO KNO in reply to MMark, 01-22-2005 07:57:05  
Another good place to look is the thermodynamics book, as it has an equation for the thermodynamic efficiency of the Otto cycle as a function of CR.

http://www.ytmag.com/cgi-bin/viewit.cgi?bd=ttalk&th=375455



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NP

01-22-2005 11:03:31




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 Re: HI-TECH COMPRESION QUESTIONS-FOR THOSE WHO KNO in reply to MMark, 01-22-2005 07:57:05  
Another good place to look is the thermodynamics book, as it has an equation for the thermodynamic efficiency of the Otto cycle as a function of CR.



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Marty in Mi.

01-22-2005 05:23:22




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 Re: HI-TECH COMPRESION QUESTIONS-FOR THOSE WHO KNO in reply to Clarence Barenie, 01-21-2005 19:23:00  
Clarence, I wish you wouldn't ask questions like this. After reading your post, I was forced to put my boots on and go out to my garage and dig up my notes from 1984 when I did a simular experiment with my F-14. I had just put a .125 over-bore kit in and I was getting 23.5 hp. I was pretty much King of the hill in our area at that time in the 3000# class, but on a good track, I couldn't quite spin out before I ran out of power. My 3.125X4.000 bore and stroke netted me with a 122.72 c.i.d. The combustion chamber volume, including head gasket, was 30.68 c.i.d. 122.72 plus 30.68 divided by 30.68 gave me a 5:1 compression ratio. Needless to say, I was not happy with my results, so off came the head and pan, out came the pistons, and on went some half inch tall 3 inch diameter slugs of aluminum. After welding them to the top of the pistons and spending some time on the lathe getting them all pretty close to the same size(looked like a Hemi piston), I ended up losing 12.21 cubic inches of combustion chamber volume. 30.68-12.21=18.47 cid of combustion chamber volume. 122.72 plus 18.47 divided by 18.47=7.64:1 comp. ratio. This netted me with 30.5 hp. at 540.It used to pick up about 3 hp. when you lugged it down to 400 rpm before the slugs,now it picked up just shy of 6 on the dial.I did not have a M&W calculator at the time,and it's too cold to go back out to the garage and get mine this morning,so I can't say for sure what the hp. readings actually were at 400 rpm,but the difference on the track was amazing. I could now spin out in 2nd gear at 3000# and also spin out in low gear at 3500#. By the way, I did not change anything else on the engine. This actually was a descently efficient engine combination,making about .25 hp. per cubic inch. Got to run for now, looks like we got about 6 inches of snow last night,and I've got to put the snow-blower on the mighty Wheel Horse. Marty

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stroker88

01-22-2005 04:30:55




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 Re: HI-TECH COMPRESION QUESTIONS-FOR THOSE WHO KNO in reply to Clarence Barenie, 01-21-2005 19:23:00  
more compression = more hp across the board. you will have to make changes in the fuel mixture,ingnition timing,sometimes timing isn"t a problem if you create squelch area. most stock tractors didn"t have this.



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ChadS

01-21-2005 20:02:35




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 Re: HI-TECH COMPRESION QUESTIONS-FOR THOSE WHO KNO in reply to Clarence Barenie, 01-21-2005 19:23:00  
Yes, it picks up all the above, low compression is a lower efficency than a higher compressed more efficent cubic inch, bigger explosion in the cyl more HP. Cubes do help add power, but so does compression. You will have to change the carb jetting, so you cant leave the carb alone. changing compression changes a few other factors in the engine too. ChadS



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Clarence Barenie

01-23-2005 17:32:12




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 Re: HI-TECH COMPRESION QUESTIONS-FOR THOSE WHO KNO in reply to ChadS, 01-21-2005 20:02:35  
I'LL READ ALL THIS AGAIN TOMORROW, DIDN;T WANT TO THINK I FORGOT YOU ALL:
JUST GOT BACK FROM INDY (DAUGHTER'S GYNASTIC'S COMPETITION) ELECTRIC TRUNK LAYCH WOULDN'T WORK LAST NIGHT, A LITTLE HY-TECH PENETRATING OIL IAN IT WAS FIXED
CLIMBED BACK IN THE CAR WITH A HEAVY PAIR OF OVERHALLS ON AND STANGED THE TURN SIGNAL ARM AND BROKE IT OFF !!

I'M PO'ED AND THE WIFE IS GONNA THINK I'M ON EHECK OF A MECHANIC !!
I BET I JUST SPENT 200BUCKS

THE REPLIES ARE GREAT THANK'S GENTLEMEN
WRITE NOW I'M LOOKING FOR SOME GASOLINE TO BURN THESE CLOTHES I GOT ON !

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